The present invention relates generally to thermal insulation tiles and more particularly to a method for bonding thermal insulation tiles.
Thermal insulation tiles, such as those used to insulate the space shuttle orbiter, are typically formed from low-density fibrous materials having extremely high temperature resistance and a relatively low coefficient of thermal expansion as compared to metals. These materials are well known in the art and include, for example, FRCI (fibrous refractory composite insulation) and AETB (alumina enhanced thermal barrier) materials.
In fabricating the tiles, fibers of an insulating material, such as silica, alumina boro-silicate and alumina, are mixed with water to form a slurry. The slurry is deposited into a casting tower where the water is drained and the silica fibers are subjected to compressive forces to form a raw block of insulation material having a cross-sectional area that may range from 144 square inches to almost 576 square inches depending upon the dimensions of the casting tower. The raw block is then dried in an oven and subsequently fired (sintered) to bond the fibers of the insulating material together. Thereafter, tiles are formed from the fired block through conventional machining processes wherein tiles of a desired shape are cut from the solid block.
One drawback associated with this process is the maximum size of the tiles that can be formed. As the surface of the space shuttle orbiter, for example, is relatively large, it is highly desirable to form the tile as large as possible so as to reduce the labor that is required to affix the tiles to the orbiter, as well as minimize the use of the material which bonds the tiles to the orbiter to thereby minimize the weight of the orbiter""sthermal protection system. In covering a leading or trailing edge of a craft, a tile having a length in excess of 6 feet is highly desirable.
To some extent, the size of the tiles may be increased by enlarging the size of the casting tower. In practice, however, casting towers that produce raw blocks having dimensions greater than 22xe2x80x3xc3x9722xe2x80x3xc3x977xe2x80x3 inches are not practical due to the increased rate at which defects and other problems are encountered in the manufacturing process. Problems such as weight associated with transporting a large block filled with water, the inability to completely dry very large raw blocks, overheating the exterior portion of the raw block during the firing operation and underheating the interior portion of the raw block during the firing operation frequently lead to defects such as shrinking, cracking and improper bonding of the fibers. As the material that is used to form the raw blocks is relatively expensive, the increased rate of defects renders the formation of relatively large fired blocks commercially impracticable.
Another drawback associated with the previously known methods of forming tiles concerns the manner in which tiles having a complex shape are formed. Tiles which are relatively flat and sized approximately equal to the cross-section of the fired block are relatively easy to machine with little waste. Tiles having a complex shape, however, are routinely carved from a fired block, with the remainder of the fired block being discarded as scrap. As mentioned above, the material that is used to form the raw blocks is relatively expensive. Consequently, tiles that are produced in a process wherein large amounts of the fired blocks are scrapped are extremely costly to produce.
Accordingly, there remains a need in the art for a method for forming relatively large insulation tiles. There also remains a need in the art for a method for forming a complex shaped insulation tile which produces relatively less scrap. There also remains a need in the art for a method for bonding insulation tiles together.
In one preferred form, the present invention provides an insulative body having first and second porous insulation members and a binder. Each of the first and second porous insulation members is formed of a fibrous, low-density silica-based material and cooperatively defines a joint. The binder is disposed between a pair of mating surfaces that form the joint. The binder couples the first and second porous insulation members together.
In another preferred form, the present invention provides a method for coupling a first porous insulation member to a second porous insulation member wherein each of the first and second porous insulation members are formed of a fibrous, low-density silica-based material. The method includes the steps of: providing an ceramic/organic thermal setting binder having a thermal set organic binder and a ceramic binder; applying the ceramic/organic thermal setting binder between a pair of mating surfaces formed into the first and second porous insulation members; heating the first and second porous insulation members to a first predetermined temperature to initially cause the thermal set organic binder distribute the ceramic binder through a joint formed by the mating surfaces of the first and second porous insulation members and thereafter cure the organic binder to form a well bonded joint; heating the bonded first and second porous insulation members to a second predetermined temperature to bum out the thermal set organic binder; and firing the bonded first and second porous insulation members at a third predetermined temperature to cause the ceramic binder to fixedly couple the mating surfaces of the first and second porous insulation members to one another.